Condensers are used in a variety of situations for at least partially condensing a liquid from a fluid mixture. Many condensers, such as those found in automobiles, condense an entirely vapor flow into an entirely liquid flow. Typically, in such condensers, the fluid is a vapor at the inlet and a condensed liquid at the outlet. However, there are also condensers that only partially condense a fluid or condense only one constituent of gas mixture whereby the outlet contains both liquid and gas.
Condensers are also useful in a variety of other applications for recovering a liquid from an exhaust stream. One specific example of where such a condenser may be employed is in combination with a fuel cell system for recovering water from the cathode exhaust of the fuel cell. Specifically, the cathode exhaust from a polymer electrolyte membrane (PEM) fuel cell contains water that was input into the system for humidification as well as water that was produced by the electrochemical reactions within the fuel cell itself.
Most PEM fuel cells combine hydrogen gas on the anode side with oxygen on the cathode side to create water while harnessing electrons to create electricity. The reaction on the anode side of the fuel cell is [H2→2H++2e−]. The hydrogen ions permeate across the separating membrane while the electrons pass through an electronic circuit over to the cathode side. At the cathode side of the fuel cell the reaction is [2H++2e−+½O2→H2O] whereby the hydrogen ions, electrons and oxygen combine to create water. Therefore, the overall reaction theoretically produces one molecule of water per molecule of hydrogen.
Furthermore, fuel cells generally require water, in the form of humidification, for optimal performance of the membrane used in each fuel cell. Typically, one or both sides of the fuel cell, the anode and the cathode, are humidified via the respective inlet flows to maintain the hydrogen ion permeation from the anode to the cathode. Generally, air is utilized as the source of oxygen for the electrochemical reaction on the cathode side of the fuel cell, and for that reason a significant amount of water must also be used to maintain the appropriate level of humidification. A significant amount of water is required because the flow rate of air required is generally large compared to a pure oxygen flow to achieve the reaction required amount of oxygen, and/or because water overspray may be required and collected at cathode exhaust. Therefore, the fuel cell itself requires a significant amount of humidification to operate.
As alluded to previously, the fuel cell creates water as a product of the electrochemical reaction. Therefore, not only does the cathode exhaust have water from the inlet humidification, but the fuel cell produces water as well. To maximize the efficiency of the fuel cell system, it is desirable to recover the water from the cathode exhaust to use for humidification and/or for cooling in other parts of the fuel cell system.
In this regard, condensers are frequently employed to recover water from the cathode exhaust. Because the temperature of the condensed and entrained water may be higher than the desired temperature, others have chosen to combine a condenser in series with a liquid cooler.
However, using a condenser in series with a liquid cooler contributes to pressure drops through the multiple units. Additionally, even with an upstream water separator, the pressure drop can be too great, possibly requiring additional pumps. These additional pumps add to overall parasitic losses and decrease overall system efficiency. Additionally, multiple units require additional space. As fuel cell systems attempt to become smaller and smaller for automobile applications and the like, it is desirable to provide a smaller condensing unit. Therefore, there exists the need for a cathode exhaust condenser, a liquid/gas separator and liquid cooler that minimize gas pressure losses and/or minimize overall space requirements